Semiconductor apparatus having conductive layers and semiconductor thin films

ABSTRACT

A semiconductor apparatus includes a substrate; m electrically conductive layers formed on the substrate, m being an integer of 2 or more, potentials of the m electrically conductive layers being capable of being independently controlled; and semiconductor thin films having at least one semiconductor device respectively. The semiconductor thin films are bonded on surfaces of the m electrically conductive layers respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor apparatus useful in,for example, a light-emitting diode (LED) print head in anelectrophotographic printer.

2. Description of the Related Art

FIG. 19 is a perspective view schematically showing a part of aconventional LED print unit, and FIG. 20 is a plan view showing a partof an LED array chip provided to the LED print unit of FIG. 19.Referring to FIG. 19, a conventional LED print unit 900 includes acircuit board 901 on which are mounted a plurality of LED array chips902 having electrode pads 903, and a plurality of driving integratedcircuit (IC) chips 904 having electrode pads 905. The electrode pads 903and 905 are interconnected by bonding wires 906 through which current issupplied from the driving-IC chips 904 to LEDs 907 formed in the LEDarray chips 902. Further electrode pads 909 on the driving-IC chips 904are connected to bonding pads 910 on the circuit board 901 by furtherbonding wires 911.

For reliable wire bonding, the electrode pads 903, 905, and 909 must becomparatively large, e.g., one hundred micrometers square (100 μm×100μm), and the LED array chips 902 must have approximately the samethickness as the driving-IC chips 904 (typically 250-300 μm), eventhough the functional parts of the LED array chips 902 (the LEDs 907)have a depth of only about 5 μm from the surface. To accommodate theneeds of wire bonding, an LED array chip 902 must therefore be muchlarger and thicker than necessary simply to accommodate the LEDs 907.These requirements drive up the size and material cost of the LED arraychips 902.

As shown in plan view in FIG. 20, the electrode pads 903 may need to bearranged in a staggered formation on each LED array chip 902. Thisarrangement further increases the chip area and, by increasing thelength of the path from some of the LEDs 907 to their electrode pads903, increases the associated voltage drop.

The size of the driving-IC chips 904 also has to be increased toaccommodate the large number of bonding pads 905 by which they areinterconnected to the LED array chips 902.

Light-emitting elements having a thin-film structure are disclosed inJapanese Patent Laid-Open Publication No. 10-063807 (FIGS. 3-6, FIG. 8,and paragraph 0021), but these light-emitting elements have electrodepads for solder bumps through which current is supplied. An array ofsuch light-emitting elements would occupy substantially the same area asa conventional LED array chip 902.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductorapparatus having conductive layers and semiconductor thin films, whereinthe apparatus can reduce its size and material cost.

According to the present invention, a semiconductor apparatus includes asubstrate; m electrically conductive layers formed on the substrate, mbeing an integer of 2 or more, potentials of the m electricallyconductive layers being capable of being independently controlled; andsemiconductor thin films having at least one semiconductor devicerespectively, the semiconductor thin films being bonded on surfaces ofthe m electrically conductive layers respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached drawings:

FIG. 1 is a perspective view schematically showing a part of anintegrated LED/driving-IC chip in accordance with a first embodiment ofthe present invention;

FIG. 2 is a plan view schematically showing a part of the integratedLED/driving-IC chip of the first embodiment;

FIG. 3 is a schematic cross sectional view showing a cross sectionthrough line S₃-S₃ in FIG. 2;

FIG. 4 is a circuit diagram of the integrated LED/driving-IC chip of thefirst embodiment;

FIG. 5 is a schematic cross sectional view for explaining a firstprocess of fabricating an LED epitaxial film of the first embodiment;

FIG. 6 is a schematic cross sectional view for explaining a secondprocess of fabricating an LED epitaxial film of the first embodiment;

FIG. 7 is a schematic cross sectional view for explaining a thirdprocess of fabricating an LED epitaxial film of the first embodiment;

FIG. 8 is a schematic cross sectional view showing a cross sectionthrough line S₈-S₈ in FIG. 7;

FIG. 9 is a perspective view schematically showing an integratedLED/driving-IC chip in accordance with a modification of the firstembodiment;

FIG. 10 is a perspective view schematically showing a part of anintegrated LED/driving-IC chip in accordance with a second embodiment ofthe present invention;

FIG. 11 is a plan view schematically showing a part of the integratedLED/driving-IC chip of the second embodiment;

FIG. 12 is a schematic cross sectional view showing a cross sectionthrough line S₁₂-S₁₂ in FIG. 11;

FIG. 13 is a perspective view schematically showing a part of anintegrated LED/driving-IC chip in accordance with a third embodiment ofthe present invention;

FIG. 14 is a plan view schematically showing a part of the integratedLED/driving-IC chip of the third embodiment;

FIG. 15 is a perspective view schematically showing the integratedLED/driving-IC chip of the third embodiment;

FIG. 16 is a perspective view for explaining a process of fabricatingthe integrated LED/driving-IC chip of the third embodiment;

FIG. 17 is a schematic cross sectional view showing an LED print headequipped with the semiconductor apparatus of the present invention;

FIG. 18 is a schematic cutaway side view of an LED printer employing theinvented semiconductor apparatus;

FIG. 19 is a perspective view schematically showing a part of aconventional LED print unit; and

FIG. 20 is a plan view schematically showing a part of an LED array chipprovided in the LED print unit of FIG. 19.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described with reference to theattached drawings, in which like elements are indicated by likereference characters.

First Embodiment

FIG. 1 is a perspective view schematically showing a part of anintegrated LED/driving-IC chip 100 as a semiconductor apparatus inaccordance with a first embodiment of the present invention. FIG. 2 is aplan view schematically showing a part of the integrated LED/driving-ICchip 100 of the first embodiment, and FIG. 3 is a schematic crosssectional view showing a cross section through line S₃-S₃ in FIG. 2.FIG. 4 is a circuit diagram of the integrated LED/driving-IC chip 100 ofthe first embodiment.

As shown in FIGS. 1 to 4, an integrated LED/driving-IC chip 100 of thefirst embodiment includes a silicon (Si) substrate 101 having anintegrated circuit 102, and m (m being an integer of 2 or more) metallayers 103 formed on the Si substrate 101 so that potentials of themetal layers 103 are capable of being independently controlled. Theintegrated LED/driving-IC chip 100 also includes epitaxial films 104 assheet-like semiconductor thin films, which are bonded on the associatedm metal layers 103 respectively. Each epitaxial film 104 has n (n beingan integer of 2 or more) LEDs 105. The integrated LED/driving-IC chip100 further includes a plurality of individual interconnecting lines106, each of which extends from an upper surface of the LED 105 to anupper surface of an individual electrode region 107 of the Si substrate101.

As shown in FIGS. 2 to 4, further, the integrated LED/driving-IC chip100 of the first embodiment also includes m common wiring lines 131provided in the integrated circuit 102 so that potentials of the commonwiring lines 131 are capable of being controlled independently of eachother, and n signal wiring lines 132 provided in the integrated circuit102 so that potentials of the signal wiring lines 132 are capable ofbeing controlled independently of each other. The m common wiring lines131 and the n signal wiring lines 132 are electrically connected to adriving-IC 109, which may be a part of the integrated circuit 102 or aseparate device electrically connected to the integrated circuit 102.The driving-IC 109 independently controls the potentials of the m commonwiring lines 131 and the potentials of the n signal wiring lines 132.The m common wiring lines 131 and the m electrically conductive layers103 are electrically connected to each other in a one-to-onecorrespondence. For this reason, the driving-IC 109 can independentlycontrol the potentials of the m electrically conductive layers 103. Forexample, the driving-IC 109 can selectively connect the m electricallyconductive layers 103 to ground. Therefore, the driving-IC 109 cancontrol potentials of the LEDs 105 on the side of the common electrodes.

The k-th one (k=1, 2, . . . , n) of the n LEDs 105 provided on each ofthe m electrically conductive layers 103 is electrically connected tothe k-th one of the n signal wiring lines 132, where k indicates anorder in an array of the n LEDs 105 or an arrangement of the n signalwiring lines 132. Therefore, the k-th one of the nsecond-conductive-type semiconductor layers and the k-th one of the nsignal wiring lines 132 are electrically connected to each other in aone-to-one correspondence. For this reason, the driving-IC 109 canindependently control the potentials of the n signal wiring lines 132,and thus can control potentials of the LEDs 105 on the side of theindividual electrodes. Although FIG. 4 shows a case of m=4 and n=4, thevalues of m and n are not restricted to such values.

As shown in FIGS. 1 to 3, the n LEDs (also referred to below aslight-emitting parts or regions) 105 formed in the LED epitaxial films104 are arranged in a row at regular intervals. The n LEDs 105 may notbe arranged at regular intervals. Furthermore, the arrangement of the nLEDs 105 is not limited to a single row, but the n LEDs 105 may bearranged as regularly shifted in a direction perpendicular to adirection of the arrangement of the n LEDs 105. Further, as shown inFIG. 2, the LED epitaxial films 104 have a width W₁ larger than a widthW₂ of the light-emitting regions of the LEDs 105. For example, the widthW₂ of the light-emitting regions of the LEDs 105 is set to be 20 μm, andthe width W₁ of the LED epitaxial films 104 is set to be 50 μm, so thata margin of 15 μm is provided to each of both sides of thelight-emitting regions 105. The width W₁ of the LED epitaxial films 104is much smaller than width (typically, about 400 μm) of a substrate ofthe conventional LED print head having electrode pads. However, thewidth W₁ of the LED epitaxial films 104 and the width W₂ of thelight-emitting regions of the LEDs 105 are not limited to theaforementioned values.

It is desirable that the LED epitaxial film 104 be made of onlyepitaxial layers to be explained later. The thickness of the LEDepitaxial film 104 may be about 2 μm that is sufficient to secure stablecharacteristics (e.g., light-emitting characteristics or electricalcharacteristics) of the LED. The thickness of the LED epitaxial film 104is much smaller than the thickness (typically, about 300 μm) of theconventional LED print head. As the thickness of the LED epitaxial film104 is increased, a disconnection due to poor step coverage tends toprobably occur in the thin-film wiring layer (e.g. the individual wiringlines 106) formed on the LED epitaxial film 104. In order to avoidoccurrence of the disconnection, it is desirable that the LED epitaxialfilm 104 have a thickness of about 10 μm or less. In this connection, bytaking measures, e.g., to planarize the stepped zone with use ofinsulating material such as polyimide, it is also possible to set thethickness of the LED epitaxial film 104 to exceed 10 μm.

The Si substrate 101 is a monolithic Si substrate, in which theintegrated circuit 102 is formed. The integrated circuit 102 includes aplurality of driving-ICs for driving the LEDs 105 formed in the LEDepitaxial film 104. Besides the driving circuits, the integrated circuit102 includes shared circuitry for illumination control of the LEDs 105.The Si substrate 101 has a thickness of about 300 μm, for example. Theother materials such as amorphous silicon, single crystal silicon,polysilicon, compound semiconductor, organic semiconductor, andinsulating material (such as glass or sapphire) can be used as thesubstrate material. In addition, the Si-substrate 101 including theintegrated circuit 102 can be replaced, for example, by an insulatingsubstrate and an integrated circuit device (109 in FIG. 4) mountedthereon.

The metal layers 103 are formed on the surface of the substrate 101 in aregion adjacent to but not overlapping the part in which the integratedcircuit 102 is formed. The metal layers 103 are, for example, palladiumor gold films with a thickness of about one hundred nanometers (100nm=0.1 μm). The LED epitaxial films 104 are bonded to the surfaces ofthe metal layers 103. The functions of the metal layers 103 include bothbonding the LED epitaxial films 104 on the surface of the substrate 101and electrical connecting a common electrode layer of the bottom surfaceof the LED epitaxial film to a common electrode area on the Si substrate101. It is desirable that an ohmic contact be created between the metallayers 103 and the common electrode area of the bottom surface of theLED epitaxial film 104 and between the metal layers 103 and the commonelectrode area (e.g., reference numeral 108 in FIG. 2) of the Sisubstrate 101. The common electrode areas of the LED epitaxial films 103in this embodiment is an n-type GaAs layer 111 that occupies the entirebottom surface of the LED epitaxial film. The common electrode layer ofthe Si substrate 101 indicates the entire surface of the Si substrate101 contacting the metal layers 103 provided on the Si substrate 101.The metal layers 103 may be formed on the surface of the Si substrate101 in a region where the integrated circuit 102 is formed (so as towholly or partly overlapped therewith) while providing an insulatinglayer between the metal layer 103 and the surface of the Si substrate101.

As shown in FIGS. 2 and 4, the individual interconnecting lines 106electrically connect upper surfaces of the light-emitting regions 105 ofthe LED epitaxial films 104 and the individual electrode regions 107 ofthe Si substrate 101. The individual interconnecting lines 106 may beformed by patterning a thin electrically conductive film such as a metalfilm. Specific examples of suitable films of the individualinterconnecting lines 106 include (1) a film containing gold (Au), e.g.,a single-layer gold film, a multi-layer film with titanium, platinum,and gold layers (a Ti/Pt/Au film), a multi-layer film with gold and zinclayers (an Au/Zn film), or a multi-layer film with a gold layer and agold-germanium-nickel layer (an AuGeNi/Au film); (2) a film containingpalladium (Pd), e.g., a single-layer palladium film or a multi-layerfilm with palladium and gold layers (a Pd/Au film); (3) a filmcontaining aluminum (Al), e.g., a single-layer aluminum film or amulti-layer film with aluminum and nickel layers (an Al/Ni film); (4) apolycrystalline silicon (polysilicon) film; (5) a thin, electricallyconductive oxide film such as an indium tin oxide (ITO) film or a zincoxide (ZnO) film.

In each of the individual interconnecting lines 106, the material of acontact part with the LED 105 may be different from the material of theother part. In this case, the above metal material and electricallyconductive oxide materials may be suitably combined and used. All of theindividual interconnecting lines 106 can be formed simultaneously. Whenthe individual interconnecting lines 106 are formed from a thin film,since their width is restricted by the array pitch of the LEDs 105, asignificant voltage drop will occur if the individual interconnectinglines 106 are too long. When several milliamperes of driving current issupplied through an individual interconnecting line 106 that is 5 μmwide and 0.5 μm thick, for example, length of the individualinterconnecting line is preferably less than about 200 μm.

An interdielectric thin film is provided in a region where electricshort-circuiting should be avoided, for example, between the individualinterconnecting lines 106 and top- and side-surface of the LED epitaxialfilms 104, between the individual interconnecting lines 106 and themetal layers 103, between the individual interconnecting lines 106 andthe surface of the Si substrate 101, between the individualinterconnecting lines 106 and the surface of the Si substrate 101 in theregion where the integrated circuit 102 is formed, or the like, therebysecuring normal operation. The individual interconnecting lines 106 mustcross steps, such as the step at the edge of the metal layer 103 andsteps at the edges of openings in the interlayer dielectric film. Toprevent short- and open-circuit faults in the individual interconnectinglines 106 at these steps, the interlayer dielectric film is preferablyformed by a method such as a plasma chemical vapor deposition (P-CVD)method that provides good step coverage. The steps may also beplanarized with a polyimide film, a spin-on-glass film, or otherinterdielectric thin film (e.g., silicon oxide or silicon nitride).

The cross sectional structure of the first embodiment will next bedescribed. Referring to FIG. 3, the integrated LED/driving-IC chip 100has a structure of the Si substrate 101, the metal layer 103, the LEDepitaxial film 104, and the individual interconnecting line 106, whichare formed in this order. Referring to FIG. 3, the LED epitaxial film104 includes, from the bottom up, an n-type gallium arsenide (GaAs)layer 111 and three n-type aluminum gallium arsenide (AlGaAs) layers: anAl_(x)Ga_(1-x)As lower cladding layer 112 (0≦x≦1), an Al_(y)Ga_(1-y)Asactive layer 113 (0≦y≦1), and an Al_(z)Ga_(1-z)As upper cladding layer114 (0≦z≦1). A second n-type GaAs contact layer 115 is formed on then-type Al_(z)Ga_(1-z)As layer 114 and then p-type impurity of zinc (Zn)is selectively diffused into the epitaxial layers so that theZn-diffusion front is in the active layer 113. The insulating thin film117 is formed to cover the upper surface of the substrate and theindividual electrode 106 is formed on the p-type (Zn-diffused) contactlayer 115. Light is emitted when forward current is supplied across thepn junction between the p-type and n-type regions.

The n-type GaAs layer 111 is about 10 nm (0.01 μm) thick, the n-typeAl_(x)Ga_(1-x)As lower cladding layer 112 about 0.5 μm thick, the n-typeAl_(y)Ga_(1-y)As active layer 113 about 1 μm thick, the n-typeAl_(z)Ga_(1-z)As upper cladding layer 114 about 0.5 μm thick, and thep-type GaAs contact layer 115 about 10 nm (0.01 μm) thick. The totalthickness of the LED epitaxial film 104 is about 2.02 μm.

The aluminum composition ratios x, y, z of the AlGaAs layers arepreferably selected so that x>y and z>y (e.g., x=z=0.4, y=0.1), and thediffusion front of the zinc diffusion region 116 is preferably locatedwithin the n-type Al_(y)Ga_(1-y)As active layer active 113. In thisstructure, minority carriers injected through the pn junction areconfined within the n-type Al_(y)Ga_(1-y)As active layer 113 and thep-type Al_(y)Ga_(1-y)As region created therein by zinc diffusion, sothat high luminous efficiency is obtained. The structure shown in FIG. 3enables high luminous efficiency to be obtained with an LED epitaxialfilm 104 as thin as about 2 μm.

The LED epitaxial film 104 is not limited to thicknesses or materialsgiven above. Other materials, such as an aluminum-gallium indiumphosphide ((Al_(x)Ga_(1-x))_(y)In_(1-y)P, where 0≦x≦1 and 0≦y≦1, agallium nitride (GaN), an aluminum gallium nitride (AlGaN), and anindium gallium nitride (InGaN), may also be employed. Other than adouble hetero-epitaxial structure described in FIG. 3, a singlehetero-epitaxial structure and a homo-epitaxial structure can be alsoapplied in LEDs.

Next, a fabrication process for the LED epitaxial film 104 will bedescribed with reference to FIGS. 5 to 8, which are schematic crosssectional views for explaining process of fabricating an LED epitaxialfilm of the first embodiment. Further, FIG. 8 shows a cross sectionthrough line S₈-S₈ in FIG. 7, and FIG. 7 shows a cross section throughline S₇-S₇ in FIG. 8.

Referring to FIG. 5, the fabrication process begins with the formationof an LED epitaxial layer 104 a on a fabrication substrate 120 by thetechniques such as metal organic chemical vapor deposition (MOCVD) ormolecular beam epitaxy (MBE). After lifting off the LED epitaxial layer104 a, it becomes the LED epitaxial film 104. The fabrication substrate120 in FIG. 5 includes a GaAs substrate 121, a GaAs buffer layer 122, analuminum-gallium indium phosphide ((AlGa)InP) etching stop layer 123,and an aluminum arsenide (AlAs) sacrificial layer 124. The n-type GaAscontact layer 111, n-type Al_(x)Ga_(1-x)As lower cladding layer 112,n-type Al_(y)Ga_(1-y)As active layer 113, n-type Al_(z)Ga_(1-z)As uppercladding layer 114, and n-type GaAs contact layer 115 a are formed inthis order on the AlAs sacrificial layer 124, creating an LED epitaxiallayer 104 a. Lifting-off of the LED epitaxial layer 104 a can be carriedout by a chemical lift off method. Furthermore, the (AlGa)InP etchingstop layer 123 can be omitted.

A diffusion mask layer (dielectric film) is formed on the LED epitaxiallayer 104 a and openings are created. P-type impurity comprising zinc(Zn) is diffused through the openings by, for example, solid-phasediffusion to create the zinc diffusion regions 116. The diffusion sourcefilm (not shown in the figures) used for the solid-phase diffusionprocess is then removed to expose the surface of the GaAs contact layer115 in the zinc diffusion regions 116. Due to the p-type impuritydiffusion, the n-type GaAs contact layer 115 has become a p-type GaAscontact layer in these diffusion regions. Part of the second GaAs layer(115 a) including pn-junction is etched to remove.

Referring to FIG. 6, an interlayer dielectric film 117 is now formed,openings are created therein.

As shown in FIGS. 7 and 8, the AlAs sacrificial layer 124 is selectivelyremoved with use of a 10% HF (hydrogen fluoride) solution. Since anetching rate for the AlAs sacrificial layer 124 is much larger than anetching rate for the AlGaAs layers 112 to 114, GaAs layers 111, 121,122, and etching stop layer 123; the AlAs sacrificial layer 124 can beselectively etched. As a result, the LED epitaxial layer 104 a (LEDepitaxial film 104) can be lifted off from the LED epitaxial filmfabrication substrate 120.

In this connection, for the purpose of making the LED epitaxial film 104thin and also to lift off the LED epitaxial film 104 from the LEDepitaxial film fabrication substrate 120 in a comparative short time, itis desirable that the LED epitaxial film 104 have a width of 300 μm orless, e.g., about 50 μm. To this end, as shown in FIG. 8, the respectiveepitaxial layers 111 to 114 and 115 a are previously etched so thattrenches 125 are made therein and the layers have a width W₁ of 50 μm.The formation of the trenches 125 are carried out by photolithographyfor masking the epitaxial layers with use of resist for the trenchformation and etching the epitaxial layers using a phosphate peroxideetchant (i.e., a solution of phosphoric acid and hydrogen peroxide). Forsimplicity, only one trench 125 is shown in FIG. 8. The phosphateperoxide etchant etches the AlGaAs layers 112 to 114 and GaAs layers111, 115 a, 121, 122. However, since the etching rate of the etchant forthe etching stop layer 123 is low, the trench 125 formed from the uppersurface can be prevented from arriving at the GaAs substrate 121 duringthe etching. The trench 125 may be formed after removing part of theinterdielectric thin film on the trench formation area. The removingprocess of part of the interdielectric thin film may be carried outusing a resist mask for formation of the trench 125. After the trench125 is formed, the AlAs sacrificial layer 124 is etched using the HFsolution and then the LED epitaxial film 104 is lifted off. Although theAlAs sacrificial layer 124 is illustrated as still remain (as etchedhalfway) in FIG. 8, the AlAs sacrificial layer 124 is completely removedin such a condition as to carry the LED epitaxial film 104. After theAlAs sacrificial layer 124 has been completely removed by etching, theLED epitaxial film 104 is immersed in deionized water so that no etchingsolution residue remains. When lifting off the LED epitaxial film 104, asupporting material for carrying and protecting the LED epitaxial filmcan be provided on the LED epitaxial film 104. For example, when thesupporting material is provided on the LED epitaxial film 104, thesupporting material can be transferred to a predetermined position bysucking the surface of the supporting material by vacuum suction orbonding the surface of the supporting material by a photo-hardeningadhesive sheet, which hardens and loses its adhesive property whensubjected to light irradiation.

In the integrated LED/driving-IC chip 100 of the first embodiment, sinceit is not necessary to provide electrode pads for wire bonding on theLED epitaxial film 104, space can be saved and the area occupied by theLED epitaxial film 104 can be much smaller than the area occupied by aconventional LED array chip. Furthermore, since the LED epitaxial film104 is supported by the Si substrate 101 and need not be thickened toprovide strength for wire bonding, it can be much thinner than aconventional LED array chip. These effects lead to a substantialreduction in material costs.

In the integrated LED/driving-IC chip 100 of the first embodiment,furthermore, when compared with a system having a driver circuit foreach LED, the surface area of the integrated circuit 102 can bedecreased.

In the integrated LED/driving-IC chip 100 of the first embodiment, inaddition, the common wiring lines 131 and signal wiring lines 132requiring a large surface area are provided not on the LED epitaxialfilms 104 made of expensive compound semiconductor but on the Sisubstrate 101 or within the Si substrate 101. As a result, the materialcost can be reduced.

FIG. 9 is a perspective view schematically showing an integratedLED/driving-IC chip 150 as a semiconductor apparatus in accordance witha modification of the first embodiment of the present invention. In FIG.9, parts that are the same as or correspond to those in FIG. 1 (firstembodiment) are denoted by the same reference numerals. The integratedLED/driving-IC chip 150 shown in FIG. 9 is different from that of FIG. 1in the shape of metal layers 153. In FIG. 1, the metal layers 103 areelectrically connected with the common electrode regions 108 (electrodearea extending from the integrated circuit 102) of the Si substrate 101.In FIG. 9, on the other hand, extensions 153 a of the metal layers 153are extended up to the upper surface of the common electrode region ofthe integrated circuit 102. The example of FIG. 9 is the same as theaforementioned first embodiment shown in FIGS. 1 to 4, except for theabove-described respects. In this connection, as how to connect themetal layers 103 to the signal wiring lines 132, another method otherthan the above specific example may be employed.

Second Embodiment

FIG. 10 is a perspective view schematically showing a part of anintegrated LED/driving-IC chip 200 as a semiconductor apparatus inaccordance with a second embodiment of the present invention, and FIG.11 is a plan view schematically showing a part of the integratedLED/driving-IC chip 200 of the second embodiment. Further, FIG. 12 is aschematic cross sectional view showing a cross section through lineS₁₂-S₁₂ in FIG. 11.

In FIG. 10, parts that are the same as or correspond to those in FIG. 1(first embodiment) are denoted by the same reference numerals. In FIG.11, parts that are the same as or correspond to those in FIG. 2 (firstembodiment) are denoted by the same reference numerals. In FIG. 12,parts that are the same as or correspond to those in FIG. 3 (firstembodiment) are denoted by the same reference numerals. An integratedLED/driving-IC chip 200 shown in FIGS. 10 and 11 is different from theintegrated LED/driving-IC chip 100 of the first embodiment shown inFIGS. 1 and 2 in that n LED epitaxial films 204 are bonded on each ofthe metal layers 103 and that each LED epitaxial film 204 has a singleLED 106.

As shown in FIG. 12, the LED epitaxial film 204 has a laminatedstructure in which a p-type Al_(x)Ga_(1-x)As layer 212, a p-typeAl_(y)Ga_(1-y)As layer 213, an n-type Al_(z)Ga_(1-z)As layer 214 and ann-type GaAs layer 215 are sequentially formed, from the bottom up, on ap-type GaAs layer 211. An interdielectric thin film 117 is formed on then-type GaAs layer 215, and the individual interconnecting lines 106 areformed on a region extending from openings of the interdielectric thinfilm 117 to the individual electrode regions 107 of the integratedcircuit 102. The Al composition of each of the above layers can be setto satisfy a relation of x>y and z>y (e.g., x=z=0.4 and y=0.1). However,the structure and composition of the LED epitaxial film 204 are notlimited to such those as mentioned above. The LED shown in FIG. 12 has adouble hetero-junction structure, but it is also possible to fabricateLEDs with a single hetero-junction structure or a homojunctionstructure. Further, various types of structures including provision ofnondoped active layer between cladding layers or insertion of aquantum-well layer between in the cladding layers can be employed. Sucha modification as a p-type layer as the upper layer and an n-type layeras the lower layer is also possible.

As has been explained above, in the integrated LED/driving-IC chip 200of the second embodiment, since the LED epitaxial film 204 is dividedinto small parts, the material cost can be further reduced.

In the integrated LED/driving-IC chip 200 of the second embodiment,further, the LED epitaxial films 204 are divided to be small. As aresult, a problem with the internal stress of the LED epitaxial films204 involved when the thermal expansion coefficient of the LED epitaxialfilms 204 and the thermal expansion coefficient of the Si substrate 101are largely different, can be reduced, and thus one of factors causing adefect in the LED epitaxial films 204 can be eliminated. For thisreason, the integrated LED/driving-IC chip 200 of the second embodimentcan be increased in reliability.

In the integrated LED/driving-IC chip 200 of the second embodiment,furthermore, the LED epitaxial films 204 are divided to be small and thebonding area is small. Thus a process of tightly bonding the LEDepitaxial films 204 to the metal layers 103 can be facilitated, andtherefore a defect generation rate caused by incomplete adhesion can bedecreased.

In the integrated LED/driving-IC chip 200 of the second embodiment,furthermore, since the LED epitaxial film 204 has only light-emittingregions, the width of the LED epitaxial film 204 can be made small andthe length of the individual interconnecting lines 106 can be madeshort.

The second embodiment is substantially the same as the above firstembodiment, except for the above-described respects.

Third Embodiment

FIG. 13 is a perspective view schematically showing a part of anintegrated LED/driving-IC chip 300 in accordance with a third embodimentof the present invention, and FIG. 14 is a plan view schematicallyshowing a part of the integrated LED/driving-IC chip 300 of the thirdembodiment. Further, FIGS. 15 and 16 are perspective views schematicallyshowing a process of fabricating an integrated LED/driving-IC chip 3000f the third embodiment.

In FIG. 13, parts that are the same as or correspond to those in FIG. 1(first embodiment) are denoted by the same reference numerals. In FIG.14, parts that are the same as or correspond to those in FIG. 2 (firstembodiment) are denoted by the same reference numerals. In theintegrated LED/driving-IC chip 300 shown in FIGS. 13 and 14, ends 303 aof metal layers 303 in an LED array direction (i.e., a direction of arow of the LEDs 105) and ends of the LED epitaxial films 104 are locatedon an imaginary identical plane (not shown in the figures) perpendicularto the surface of the Si substrate 101, that is, are aligned with oneanother. For fabricating such a structure, as shown in FIG. 15, anelongated metal layer 313 before a separating process is formed on theSi substrate 101, and an LED epitaxial film 314 before the separatingprocess is bonded on the metal layer 313. Next, as shown in FIG. 16, theLED epitaxial film 314 and the metal layer 313 provided thereunder arepartially removed with use of an etching mask (not shown in the figures)to create separated metal layers 303 and separated LED epitaxial films104. Through such a process, the ends 303 a of the separated metallayers 303 and the ends of the separated LED epitaxial films 104 can bealigned with each other, as shown in FIGS. 13 and 14.

As has been explained above, in the integrated LED/driving-IC chip 300of the third embodiment, since the separated metal layers 303 can bealigned with the ends of the separated LED epitaxial films 104, nomisalignment between the ends of the metal layers 303 and the ends ofthe LED epitaxial films will take place. For this reason, a defect(e.g., a damage in the LED epitaxial films) caused by a deviation in thebonding position of the LED epitaxial films 104 can be avoided.

The third embodiment is substantially the same as the foregoing first orsecond embodiment, except for the above-described respects.

LED Print Head

FIG. 17 is a schematic cross sectional view of an LED print head 700having the semiconductor apparatus of the present invention builttherein. As shown in FIG. 17, the LED print head 700 includes a base 701on which an LED unit 702 is mounted. The LED unit 702 includes aplurality of integrated LED/driving-IC chips 702 a of the type describedin any of the preceding embodiments, mounted so that theirlight-emitting parts are positioned beneath a rod lens array 703. Therod lens array 703 is supported by a holder 704. The base 701, LED unit702, and holder 704 are held together by clamps 705. Light emitted bythe light-emitting elements in the LED unit 702 is focused by rod lensesin the rod lens array 703 onto, for example, a photosensitive drum (notshown) in an electrophotographic printer or copier.

Use of integrated LED/driving-IC chips 702 a instead of the conventionalpaired LED array chips and driver IC chips enables the LED unit 702 tobe reduced in size and reduces its assembly cost, as there are fewerchips to be mounted.

LED Printer

FIG. 18 shows an example of a full-color LED printer 800 in which thepresent invention may be employed. The printer 800 has a yellow (Y)process unit 801, a magenta (M) process unit 802, a cyan (C) processunit 803, and a black (K) process unit 804, which are mounted followingone another in tandem fashion. The cyan process unit 803, for example,includes a photosensitive drum 803 a that turns in the directionindicated by the arrow, a charging unit 803 b that supplies current tothe photosensitive drum 803 a to charge the surface thereof, an LEDprint head 803 c that selectively illuminates the charged surface of thephotosensitive drum 803 a to form an electrostatic latent image, adeveloping unit 803 d that supplies cyan toner particles to the surfaceof the photosensitive drum 803 a to develop the electrostatic latentimage, and a cleaning unit 803 e that removes remaining toner from thephotosensitive drum 803 a after the developed image has been transferredto paper. The LED print head 803 c has, for example, the structure shownin FIG. 17, including integrated LED/driving-IC chips 702 a of the typedescribed in any of the nine embodiments above. The other process units801, 802, 804 are similar in structure to the cyan process unit 803, butuse different toner colors.

The paper 805 (or other media) is held as a stack of sheets in acassette 806. A hopping roller 807 feeds the paper 805 one sheet at atime toward a paired transport roller 810 and pinch roller 808. Afterpassing between these rollers, the paper 805 travels to a registrationroller 811 and pinch roller 809, which feed the paper toward the yellowprocess unit 801.

The paper 810 passes through the process units 801, 802, 803, 804 inturn, traveling in each process unit between the photosensitive drum anda transfer roller 812 made of, for example, semi-conductive rubber. Thetransfer roller 812 is charged so as to create a potential differencebetween it and the photosensitive drum. The potential differenceattracts the toner image from the photosensitive drum onto the paper805. A full-color image is built up on the paper 805 in four stages, theyellow process unit 801 printing a yellow image, the magenta processunit 802 a magenta image, the cyan process unit 803 a cyan image, andthe black process unit 804 a black image.

From the black process unit 804, the paper 805 travels through a fuser813, in which a heat roller and back-up roller apply heat and pressureto fuse the transferred toner image onto the paper. A first deliveryroller 814 and pinch roller 816 then feed the paper 805 upward to asecond delivery roller 815 and pinch roller 817, which deliver theprinted paper onto a stacker 818 at the top of the printer.

The photosensitive drums and various of the rollers are driven by motorsand gears not shown in the drawing. The motors are controlled by acontrol unit (not shown) that, for example, drives the transport roller810 and halts the registration roller 811 until the front edge of asheet of paper 805 rests flush against registration roller 811, thendrives the registration roller 811, thereby assuring that the paper 805is correctly aligned during its travel through the process units 801,802, 803, 804. The transport roller 810, registration roller 811,delivery rollers 814, 815, and pinch rollers 808, 809, 816, 817 alsohave the function of changing the direction of travel of the paper 805.

The LED heads account for a significant part of the manufacturing costof this type of LED printer 800. By using highly reliable andspace-efficient integrated LED/driving-IC chips and enabling these chipsand the LED units in the LED heads to be manufactured by a simplifiedfabrication process with reduced material costs, the present inventionenables a high-quality printer to be produced at a comparatively lowcost.

Similar advantages are obtainable if the invention is applied to afull-color copier. The invention can also be advantageously used in amonochrome printer or copier or a multiple-color printer or copier, butits effect is particularly great in a full-color image-forming apparatus(printer or copier), because of the large number of exposure devices(print heads) required in such apparatus.

Modifications of Embodiments

Although explanation has been made in the foregoing embodiments inconnection with the case where the planarized film on the Si substrateincludes the metal layer, the metal layer 103 may be replaced by aelectrically conductive thin layer such as polysilicon, electricallyconductive oxide (ITO, ZnO), or the like.

Although explanation has been made in the foregoing embodiments inconnection with the case where the semiconductor devices provided to thesemiconductor thin films are the LEDs 105, the semiconductor device maybe another light-emitting element such as a laser, a light-sensingelement, a Hall element, or a piezoelectric element.

Explanation has been made in the foregoing embodiments in connectionwith the case where the LED epitaxial films 104 are epitaxial layers.However, a semiconductor thin film not as the epitaxial layer may beemployed in place of the LED epitaxial film.

1-16. (canceled)
 17. An optical print head including a semiconductorapparatus, the semiconductor apparatus comprising: a substrate; melectrically conductive layers formed on said substrate, m being aninteger of 2 or more, potentials of said m electrically conductivelayers being capable of being independently controlled; andsemiconductor thin films including at least one semiconductor devicerespectively, said semiconductor thin films being bonded on surfaces ofsaid m electrically conductive layers respectively.
 18. The opticalprint head of claim 17, wherein the semiconductor device in the firstthin semiconductor film in the semiconductor apparatus is alight-emitting element, the semiconductor apparatus including aplurality of such light-emitting elements, the optical print headfurther including: a base for supporting the combined semiconductorapparatus; a rod lens array for focusing the light emitted by thelight-emitting elements in the combined semiconductor apparatus; aholder for holding the rod lens array; and at least one clamp forholding the base and the holder together.
 19. An image-forming apparatuscomprising at least one optical print head including the semiconductorapparatus of claim
 17. 20. The image-forming apparatus of claim 19,further comprising: a photosensitive drum selectively illuminated by theoptical printing head to form a latent electrostatic image.
 21. Theimage-forming apparatus of claim 20, further comprising: a developingunit for supplying toner to develop the latent electrostatic image onthe photosensitive drum; and a transfer roller for transferring thedeveloped image from the photosensitive drum to printing media.
 22. Anoptical print head including a semiconductor apparatus, thesemiconductor apparatus comprising: a substrate; m electricallyconductive layers formed on said substrate, m being an integer of 2 ormore, potentials of said m electrically conductive layers being capableof being independently controlled; m semiconductor thin films, eachincluding n semiconductor devices, each semiconductor device including asecond-conductive-type semiconductor layer so that there are nsecond-conductive-type semiconductor layers, n being an integer of 2 ormore, said m semiconductor thin films being bonded on surfaces of said melectrically conductive layers respectively in a one-to-onecorrespondence; m common wiring lines disposed on said substrate,potentials of said m common wiring lines being capable of beingindependently controlled, said m common wiring lines being respectivelyelectrically connected to said m electrically conductive layers in aone-to-one correspondence; and n signal wiring lines disposed on saidsubstrate, potentials of said n signal wiring lines being capable ofbeing independently controlled; wherein said n second-conductive-typesemiconductor layers are disposed on each of said m electricallyconductive layers and are electrically connected to said n signal wiringlines so that a k-th one of said n second-conductive-type semiconductorlayers and a k-th one of said n signal wiring lines are electricallyconnected in a one-to-one correspondence, k being an integer between 1and n.
 23. An optical print head including a semiconductor apparatus,the semiconductor apparatus, comprising: a substrate; m electricallyconductive layers formed on said substrate, m being an integer of 2 ormore, potentials of said m electrically conductive layers being capableof being independently controlled; m semiconductor thin films, eachincluding n semiconductor devices, n being an integer of 2 or more, saidm semiconductor thin films being bonded on surfaces of said melectrically conductive layers respectively in a one-to-onecorrespondence; m common wiring lines disposed on said substrate,potentials of said m common wiring lines being capable of beingindependently controlled, said m common wiring lines being respectivelyelectrically connected to said m electrically conductive layers in aone-to-one correspondence; and n signal wiring lines disposed on saidsubstrate, potentials of said n signal wiring lines being capable ofbeing independently controlled; wherein said n semiconductor devices aredisposed on each of said m electrically conductive layers and areelectrically connected to said n signal wiring lines so that a k-th oneof said n semiconductor devices and a k-th one of said n signal wiringlines are electrically connected in a one-to-one correspondence, k beingan integer between 1 and n.